Optical fiber transmission systems provide a large capacity for transmitting information. Commercial optical fiber systems for telephony and data transmission were first put into use within the past few years. In spite of their recent introduction into commercial use, it is foreseeable that improved optical transmission systems will be needed. Although the transmission capacity in present systems is very high, projections show a need for even higher capacity systems in the future.
Recently dual wavelength optical sources have been discovered for wavelength multiplexing different wavelength signals onto optical fibers. This discovery occurred since methods were developed for fabricating optical fibers with very low losses across a wide range of wavelengths from 0.8 to 1.6 micrometers.
Dual wavelength optical sources are made as lasers and as light emitting diodes. Prior art optical sources are fabricated in geometric configurations which physically separate the two different light-emitting regions by tens of micrometers. The resulting beams are separated by as much as or more than the tens of micrometers.
Single mode optical fibers provide a desirable optical transmission media. The center core of a single mode optical fiber generally has a diameter of ten micrometers or less.
A problem arises when prior art dual wavelength optical sources are to be multiplexed into a single mode optical fiber. The different wavelength beams of light are separated by more than the ten micrometer diameter of the single mode optical fiber core. Therefore efficient coupling of the two different wavelength beams of light into the fiber core is difficult if not impossible.